Scholarly record

BIODIESEL PRODUCTION VIA INTERESTERIFICATION OF RAPESEED OIL WITH ALKYL ACETATE IN PRESENCE OF POTASSIUM tert-BUTOXIDE

Valdis Kampars, Kristaps Malins, Zane Sustere, Ruta Kampare

Abstract

The dominating feedstock for biodiesel production is still a vegetable oil and cost of the oil composes 80-85% of the production costs, therefore the development of the more efficient methods for biofuel production from vegetable oil remains crucial. The transesterification of oil proceeds with the production of side product: glycerol, which cannot be a part of the composition of fuel. Chemical interesterification of oil with alkyl acetate produce a mixture of fatty acid esters and triacetin. Triacetin is a fuel bio-additive and can be included in biofuel composition. Including triacetin in biofuel composition allows more efficient use of vegetable oil resources and obtain biofuel with mass from 1.1 to 1.15 times higher than the mass of oil used for its production. In order to obtain new information about the influence of chemical structure of monoester and catalyst on the interesterification in this work we have investigated reactions of rapeseed oil with methyl, ethyl, propyl, isopropyl, butyl and tert-butyl acetates in presence of potassium tert-butoxide in tert-butanol solution. The use of tert-butoxide /tert-butanol catalytic system allowed us to diminish the side reactions taking place in presence of commonly used catalyst: sodium methoxide in methanol. Also, the experimental results showed that interesterification in presence of tert-butoxide catalyst allowed increase the yield of triacetin by 12 to 14 %. The yield of fatty acid esters depended on the structure of monoester and decreased when the extension and branching of alkyl chain in alcohol moiety was present. Overall increase of the molar ratio between monoester and oil for up to 18/1 allowed to achieve the full conversion of triglyceride (excluding reactions with isopropyl acetate and tert-butyl acetate), yet did not provide reduction in the content of diacetylmonoglycerides and monoacetyldiglycerides below 8-10 %. In summary, not all the reaction mixtures met fuel characteristics standard EN 14214.

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